The invention relates to a mechanical load monitoring device for tension lines designed especially as chains, with a basic body which has a deformation part, deformable elastically until a limit load is reached and plastically after the limit load is exceeded, and two connection points, the mutual spacing of which changes under a load effect, and with an indicator member which, in the event of a deformation of the deformation part of the basic body, is transferred under the effect of spring force out of an initial position into a predetermined load indicating position, in which it remains upon cessation of the predetermined load.
A load monitoring device of the abovementioned type is known from DE-A-37 39 100. In the known device, the basic body is formed by an elliptic chain link which is integrated into a chain line and onto which is slipped an oval chain link, the clear width of which is smaller than the outer width of the elliptic chain link when the latter is not deformed. When the elliptic chain link is deformed, its outer width decreases, and, when a limit value of the outer width corresponding to an overloading of the chain line is reached, the oval chain link is pulled by a spring over the bulge of the elliptic chain link into a position signaling the overloading of the chain line.
The known device is not entirely satisfactory, inasmuch as an elongation of the elliptic chain link by a specific amount results only in a change in the outer width of this chain link by a fraction of the amount of the elongation. In other words, a diminution of the measurement quantity occurs, with the proviso that tolerance-related deviations of the assembled chain links place narrow limits on the indicating accuracy of the known device. In addition, when the known device is in practical use, there is not always a guarantee that the longitudinal axes of the assembled links are perpendicular to one another. However, an oblique position of these axes in relation to one another may lead to the undesirable phenomenon of jamming between the assembled links, which likewise has an adverse effect. Finally, the known device is not usable for indicating intermediate values.